Method of making artificially colored granules



Patented Aug. 8, 1939 I METHOD OF MAKING ARTIFICIALLY COLORED GRANULESMarion H. Veazey, Rutherford, N. J., assignor to The Patent andLicensing Corporation, New York, N. Y., a corporation of MassachusettsNo Drawing. Original application July 31, 1934,

Serial No. 737,774. Divided and this application February 23, 1938,Serial No. 191,965

2 Claims. (01. 91-70 This ap ication is a division of my copendlngchemical action rather than by a heat treatment. application Serial No.737,774, filed July 31, 1934, The insolubilization by chemical actionaffords now Patent No. 2,142,540. considerable advantage over the firstmentioned This invention relates to improvements in the method. One suchadvantage resides in the low- 5 production of artificially coloredgranules and er fuel costs in carrying on the coloring opera- 5 moreparticularly to the production of mineral tlon and another advantageresides in the abilgranules artificially colored, to be used as a surityto utilize certain pigments which cannot facing for materials subject toexposure out of readily be emp yed in the fir t m n i n d methdoors. 0dbecause of the deleterious efiect that the In its more specific aspectthe invention is conroasting temperatures have upon such pigments. 1o

cerned with the production of artificially colored The chemical methodof insolubilizing the solugranules adapted for use as a surfacing forsheet ble silicate emp y i these Processes s in material widely used asroofing, siding and for commercial practice been utilized in conjunctionsimilar purposes in building construction. With granules which are of areactive character is In the production of prepared roofing and sidwithrespect to the sodium silicate. Basic slag his the base material whichis usually a, sheet granules and other granules containing calcareoffibrous felt, is saturated and coated with asous or siliceousconstituents which, n r the Dhaltic material. The asphaltic coatinglayer conditions of operation are more or less reactive is provided witha wearing surface of mineral towards the soluble silicate, have beenutilized granules such as crushed slate, slag or the like, in this W y,makin i P i to produce arti- 20 this layer of mineral granules servingas a wearficially colored granules in W c t e So ubl ing surface andalso as a, decorativ finish for silicate becomes insolubilized atrelatively low the material. temperatures, say below 600 F., in acommer- In more recent years various m th d ha cially feasible manner.Such low temperature been suggested for the production or impositionoperations have also been carried on in the 001- 25 ofartificial colorson the surfaces of the granules orins f granules which a t n s lv Wherethe base granules are not of the desired reactive towards the solublesilicate as is the case colors, for the purpose of making it possible was a a u s. y incorporating i t largely to extend the range of colors orshades m xt f i m ili and p n wi obtainable, where otherwise the rangeis limited W i the granules are Coated, anethel nt 80 by the naturalcolor of the granules. which, under the conditions of operation, willThe more practical and economical processes cause or hasten theinsolubilization of the siliof producing so-called artificially coloredgraneateules depend upon the imposition or amxl of In the practice ofeither of the methods thus 3 pigments of desired colors to the surfacesof the generally described, the base grahwes are intro- 85 granules bymeans of soluble silicate, and mor duced into a mixer with the requisitequantities particularly sodium silicate. .The sodium silicate f the Sodim Sil and p nt and/or other in tlrese processes serves as a fixing agentfor agents that ay be incorpo the mixer binding the pigment to thegranules-,the s l bl ing continuedin operation until the surfaces ofform of the silicate being transformed in the the g a e become p e y anduniformly 40 coloring process into an insoluble state. The coated withthe coloring mixture whereupon the conversion of the soluble silicateinto an lnsoluc a d r n l s re passed through a rotary kiln ble form canbe accomplished in several ways, in order to effect the drying andinsolubilization principally two in number, and depending largeor thecoating and the fixing of the color upon ly upon the character of thebase granules that the surfaces 'of the granules. While the prac- 45 arebeing colored. In one of these methods title of the methods to which Ihave alluded rewhlch has been commercially practiced the con Suits. whenP p y Conducted. in the a version takes place under the influence ofheat tially complete insolubilizaton of the soluble ilitreatment attemperatures within the range, of cate to the point that the pigment isfirmly fixed roasting temperatures varying from 900 to 1500 and bound tothe gran the granules. Colored 50 F. In such an operation theinsolubillzation of by these processes, especially when conducted at thesodium silicate may be considered to result. the relatively lowertemperatures, havea tendpurely from the heat treatment. In the other ncyto This min manife ts itof the aforementioned methods theinsolubilizaself in the form of a white or opaque and more tion of thesodium silicate is accomplished by or less bulky deposit when thefinished granules are moistened with water and the moisture subsequentlyevaporated. Thus, when granules colored by the processes described areapplied as a surfacing layer for prepared roofing, and the roofing isexposed to the weather, particularly at temperatures around F. or less,there appears, when the rain or moisture evaporates, a white powder onthe surface of the granules. This powder or white coloration is solublein water and is washed. oif the-surface by rain and therefore is not inany sense a true or permanent discoloration, but it nevertheless rendersthe material colored with such granules objectionable to the user anddifllcultly saleable. As a matter of fact, the appearance of the whitepowder to which I have here given the designation blooming" frequentlyoccurs in shingles surfaced with such granules while the shingles arestill in the bundle in which they are shipped from the factory andbefore the shingles are applied to the roof or side wall, it theconditions under which the bundle has been shipped or stored have beensuch as to allow substantial moisture or rain to contact with thegranules.

This blooming effect, 1. e. the appearance of a deposit of white powderon the surface of the material after it has been exposed to moisture andthe moisture has subsequently evaporated is, as already stated, only atemporary condition. That is to say, the whitish powder that appears iseventually washed off on continued exposure to rain, but it reappearswith gradually diminishing intensity and finally becomes practicallyundiscernible. Nevertheless the appearance of the whitish powder on thesurface of shingles covered with the granules colored by theseprocesses, whether during shipment of the shingles or during the earlystages after exposure, militates against the saleability of theproducts.-

The principal object of my invention is to provide an improved method ofartificially coloring granules wherein use is made of soluble silicatesuch as sodium silicate as the binding or fixing agent for the coloringpigment but in which the tendency of the granules to bloom" is preventedor reduced to such a minimum degree as to make the effectunobjectionable under ordinary conditions of use.

In approaching this problem of preventing the "blooming effectdescribed, I have conducted extensive experiments in order to ascertainthe cause and the mechanism of the blooming effect and as a resultthereof I have devised means for preventing or minimizing this effect,which I shall hereinafter describe in greater detail.

From the experiments which I have conducted it appears quiteconclusively that the blooming effect is due primarily to the leachingout of sodium carbonate from the film of the coating 'material'depositedon the surfaces of the granules. When the sodium carbonate is thusleached out the subsequent evaporation of water or moisture results inthe carbonate crystallizing out as a hydrated carbonate, namely, thedecahydrate, NazCOazlOI-hO. This hydrated form of the carbonatecrystallizes out particularly at temperatures of around 55 F'. or less.The foregoingaccountsfor the fact that the blooming effect is moreeasily noticeable during the cold it gives up most of its water ofcrystallization on continued exposure to air which allows the mono- -outas follows: season of the year than during the warmer seatemperaturesfor 48 hours.

evaporation more water is added so that the hydrated sodium carbonate toremain as an opaque, very bulky deposit. The amount of decahydrate saltthat crystallizes depends not only upon the amount of sodium carbonateleached out of the film but upon the temperature prevailing duringcrystallization; the greater the amount of the decahydrate that isformed, the bulkier will be the deposit of the monohydrate when thedecahydrate subsequently undergoes its efliorescence.

In addition to the sodium carbonate present in the coloring film on thesurface of the granules, there is also present in the film certainamounts of sodium hydroxide which, when it is leached out on contactwith moisture, slowly reacts with carbon dioxide of the air, formingsodium carbonate, and the sodium carbonate thus formed appears also tobe a contributing factor to the blooming eflfect described. Inasmuch asthe sodium hydroxide must be converted to carbonate in order for it toparticipate in the formation of bloom and in view of the fact thatsodium hydroxide is highly soluble in water, its influence will belargely a matter of conditions prevailing during the first stages ofexposure. Thus if dry weather prevails for a long time considerableconversion to carbonate may take place. On the other hand if subjectedto the'action of rain, it

'appears that sodium hydroxide may be largely removed before beingconverted to carbonate.

Thus its influence is secondary and more or less casual-the major effectbeing due to the presence of carbonate already formed when the granulesare exposed to the conditions of temperature and moisture referred toabove. The blooming effect in granules as ordinarily produced,therefore, is not due to the mere presence of soluble materials in thecolored film but appears quite definitely to be dependent upon thecrystal form that the soluble materials (sodium carbonate) present inthe film take when they are leached out of the film and the water ormoisture subsequently evaporates, and upon the chemical property ofeillorescence possessed by the crystals.

The white deposit which I have termed blooming that is thus formed onthe surfaces of the granules being soluble in water and washed off byrain, nevertheless tends to reappear but is finally exhausted. Theblooming" therefore may recur over a considerable period of time.

The sodium carbonate that is present in the film apparently results fromthe reaction between the hydroxide present in the silicate solution usedin the coloring process, and carbon dioxide present in the fiue gaseswith which the granules are dried and brought to the stage ofinsolubilized silicate. The amount of the blooming" is shown by thetests which I have conducted to be directly related to the quantity ofsodium carbonate and hydroxide which can be extracted in the cold fromthe surfaces of the granules. To distinguish between granules which willbe subject to a heavy blooming and those which will show only a slight"blooming, samples of the granules need only be thoroughly wetted withwater and then dried rapidly at low temperatures. Specifically, the testis carried 50 grams of granules are placed in a standard Petrie dish ofabout 10 cms. diameter and 1 cm.

. depth, covered with approximately 25 to 35 cos.

ofdistilled water and allowed to stand at room In case of excessive fanand maintained at a temperature of to 50- F. until the granules are dry.Those on which the white deposit is heavy indi cate that the granules onexposure will suffer heavy blooming while the samples on which the Whitedeposit is small or unobservable will show' hydroxide thus extractableexceeds 0.030 gram,

considerable blooming will result. 0n the other hand when the amount ofcold extractable sodium carbonate and sodium hydroxide is below thefigures mentioned, respectively, the "blooming" will be slight ornegligible.

Although washing of the granules after they have been completelyprocessed by the so-called silicate process in order to remove allsoluble material from the film would prevent blooming, such an expedientwould necessitate the installation of costly-equipment as well asexpense in the operation thereof.

'1 have found that when the granules coated with the desired mixture ofpigment and soluble silicate have been subjected in the usual directfired kiln or retort to the elevated temperature necessary for effectinginsolubilization of themdium silicate, the tendency of the processedgranules to exhibit any substantial bloom can be eliminated by suitableafter-treatment of the thus processed granules, as hereinafter morefully described.

In an ordinary operation illustrating my invention for the production ofgreen granules from a trap rock base, the following proportions areillustrative:

Parts Trap rock granules 100 Sodium silicate 6 Chromium oxide 1 Thechromium oxide may be first suspended in the silicate and thepigment-silicate suspension may then be mixed with the granules in anysuitable form of mixer or the granules and other ingredients may beseparately introduced into the mixer, and the mixer continued inoperation until the granules become completely and uniformly coated withthe pigment-silicate suspension. The thus coated granules may then bepassed through a rotary kiln or retort of an ordinary direct fired typeand brought to the necessary temperature, say 500 to 600 F., forefiecting insolubilization of the silicate and permanent fixation of thecolor deposit on the surfaces of the granules. After the granules havethus been retorted and preferably before they have cooled, they aresubjected to treatment with substances which neutralize substantiallyall the sodium carbonate present in the film as a result of any reactionbetween sodium hydroxide and carbon dioxide of the combustion.

gases in the kiln. The amount of sodium carbonate present on granulesexhibiting a moderate to.

agent necessary to neutralize the carbonate present. Larger quantitiessufficient additionally to neutralize the sodium hydroxide can beadvantageously employed. The neutralizing agent must be selected fromamong those which do not produce water soluble bloom-formingefllorescent salts or for some other reason deposit whitish films.

These neutralizing agents are preferably used by spraying the granuleswith a water solution thereof as the granules pass from the lower end ofthe retorting kiln and pass into the cooling tower through which thegranules are usually passed in order to cool them down to thetemperature requisite for further handling. When the reagent is used inthis way it is necessary to spray the liquid so that it makes the mostefficient contact with each granule. The strength of the solution shouldbe adjusted with relation to the carbonate content of granules and theamount of aqueous solution sprayed upon the granules should be adjustedin relation to the temperature of the granules leaving the kiln. In thisway the spraying cedure, granules leaving the kiln at approximately 600F. may be sprayed with a 5 to 8% citric acid solution at a temperatureof approximately 160 F.

at such a rate that approximately 2 to 8 pounds of citric acid are usedper ton of granules. In lieu of citric acid, tartaric, and similar acidswhich do not attack the pigment and do not form water solublebloom-forming efflorescent salts may be employed. While all of theseacids appear to be effective for preventing blooming when the finishedgranules are treated therewith in the manner stated, it may be that incertain instances the effect of the acid is due to something other thanor in addition to neutralization of the carbonate and/or hydroxidepresent in the films, as for example, a tendency to'inhibit theformation of bloom-forming salt It is possible to treat the granulescold or at a reasonably elevated temperature with air-aqueous tainadditional types ofacids which are more or less volatile may be employedin lieu of or in addition to those above mentioned. For example, to oneton of granules which have been reduced to a temperature of 250 F. andcontaining about 0.1% of sodium carbonate there may be added one gallonof water containing about 3 pounds of formic, or a corresponding amountof acetic or nitric acid. The acid may be added without water, but theinclusion of water assists in the distribution of the acid and isadvantageous so long as the quantity is kept below the amount whichwould cause the granules-t0 become appreciably wet, i. e. wet enough tointerfere with their effective application as a surfacing layer forasphalt coated roofing.

In certain instances it may be desirable to utilizethe abova'describedafter-treatment of the "granules with any of the treating substancesmentioned, as anafter-treatment for/granules produced by one or more ofthe several expedients described in my co-pending application Serial No.737,774 now Patent No. 2,142,540, such as "which have been predried inan atmosphere substantially free of carbon dioxide and then retorted inthe usual way in a direct fired kiln, as also described in theaforementioned application, to an after-treatment with a spray of awater solution of a suitably selected one of the reagents hereinabovementioned.

It will be observed that the treating agents herein mentioned produce,by their reaction with sodium carbonate and/or sodium hydroxidecontained in the coated film on the granules, reaction products none ofwhich are crystallized out of water as salts of a bloom-formingcharacter. After-treatment with reagents of that character makes itpossible therefore to avoid the necessity of washing the granules toremove products of the neutralizing reaction therefrom as would be thecase if acids such as sulphuric acid were employed resulting in theproduction of sodium sulphate as one product of the neutralizingreaction which is itself of a bloom-forming character. Thus by theselection of the reagents as above described, it is unnecessary toseparately wash the treated granules to remove the reaction products ofthe neutralization and when these reagents are used in the form of asolution whose aqueous content is adjusted as above described so as tobe completely evaporated by the heat of the retorted granules, there isalso avoided the necessity for employing a subsequent separate step ofdrying the granules after neutralization has been eii'ected.

What I claim is:

1. The method of artificially coloring mineral .granules which comprisescoating the granules with pigment and sodium silicate, retorting thegranules at temperatures sufficient to insolubilize the silicate andthen neutralizing any sodium carbonate formed in the coating during theretorting of the granules by subjecting the retorted granules whilestill at an elevated temperature to treatment with an aqueous solutionof an acidic substance selected from the group consisting of citric,tartaric. formic, acetic and boric acids, said solution being applied tothe granules in amounts to enable the aqueous content to be evaporatedbythe heat of the granules.

2. The process as in claim 1, wherein the acld is employed in quantitiessuflicient to neutralize also the sodium hydroxide present in thecoating.

MARION H. VEAZEY.

